DLPI Programmer's Guide

86 Chapter 2

DLPI Primitives

Connectionless-mode Service Primitives

This section describes the connectionless-mode service primitives.

DL_UNITDATA_REQ

Conveys one DLSDU from the DLS user to the DLS provider for

transmission to a peer DLS user.

Because connectionless data transfer is an unacknowledged service, the

DLS provider makes no guarantees of delivery of connectionless

DLSDUs. It is the responsibility of the DLS user to do any necessary

sequencing or retransmission of DLSDUs in the event of a presumed

loss.

Priority messages are currently only supported over 100VG. To send a

priority message over 100VG, a user must have superuser capabilities

and set the dl_priority ﬁelds in the DL_UNITDATA_REQ primitive to

the following values:

dl_min must be set to 0.

dl_max must be set to 1.

The dl_priority ﬁeld will be ignored on interfaces which do not support

priority messages.

Format

The message consists of one M_PROTO message block containing the

structure shown below, followed by one or more M_DATA blocks

containing at least one byte of data. The amount of user data that may be

transferred in a single DLSDU is limited. This limit is conveyed by the

parameter dl_max_sdu in the DL_INFO_ACK primitive.

typedef struct {

ulong dl_primitive;

ulong dl_dest_addr_length;

ulong dl_dest_addr_offset;

dl_priority_t dl_priority;

} dl_unitdata_req_t;

Parameters

dl_primitive

DL_UNITDATA_REQ